Health concerns and related government regulations are prompting widespread use of air samplers to monitor particulate matter and other chemical species in the atmosphere. The majority of monitoring sites employ samplers operating under United States Environment Protection Agency regulations for filter sampling procedures. Filter samplers are place in the field and a constant flow of air through a preweighed filter is maintained for a set period of time, typically 24 hours. A technician visits the site after the sampling time period is completed and places a new filter in the sampler while retrieving the used filter. The used filter is brought to a laboratory where it is placed under specified constant conditions of temperature and humidity for 24 hours, and then weighed.
A major limitation of most of these samplers is that they only accommodate a single filter, requiring frequent visits to the site to change filters or multiple samplers located at the same site and timed to sample sequentially. Such solutions are expensive to implement. Presently available multiple filter sequential samplers attempt to address these problems, but do so in a way that present other difficulties both in mechanical complexity and contamination opportunities presented by unprotected filter storage within the air sampling instrument.
A need thus persists for an air sampler which can collect samples over multiple sampling periods without requiring manual intervention, involving undue mechanical complexity or compromising the air sampling process.